package com.magic.ch03_数学与简单DP.饮料换购;

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int ans = n;
        while (n > 3) {
            ans += n / 3;
            n = (n / 3) + (n % 3);
        }
        System.out.println(ans);
    }
}
